This is an investigation of purine and pyrazolopyrimidine metabolism in the culture and blood stream forms of the African trypanosomes. The methods for the study of the metabolism of these compounds will include in vivo radiolabeling of the purine metabolic pool followed by acid extraction and analysis by high pressure liquid chromatography and liquid scintillation counting. The specific activities of the various compounds in the purine metabolic pool will be used to construct computer-generated models of purine metabolism in these organisms. Pyrazolopyrimidines will be added to some experiments as inhibitors of purine metabolism. The resulting changes in specific activities of the intermediates will permit predictions, using the computer-generated model, of particular enzymes which are inhibited by these compounds. These particular enzymes will be studied in a later phase of the investigation. Aminopurinol (4-aminopyrazolo(3,4-d)pyrimidine) is incorporated into the RNA of Trypanosoma cruzi as well as the African trypanosomes. The metabolism of this compound will be investigated in the African trypanosomes and compared with its metabolism in T. cruzi in an attempt to determine the mechanism of action for the antitrypanosomal effects of allopurinol (4-hydroxypyrazolo(3,4-d)pyrimidine). The sequential conversion of allopurinol to the ribonucleotides of aminopurinol and their incorporation into RNA does not occur in mammalian cells. The last phase of this investigation will use radiolabeled tracer experiments, similar to those described above, as well as techniques for RNA isolation and characterization. In addition, two dimensional electrophoresis will be employed to characterize cellular proteins made in the presence and absence of allopurinol to measure the functional activity of RNA.